The present invention relates to a process and apparatus for forming single-sided, double-sided, or multi-layer circuit boards.
The manufacture of printed circuit boards generally follows either subtractive or additive processing techniques. According to a general subtractive process for the manufacture of printed circuit boards, a conductive layer laminated to a non-conductive substrate is selectively removed to leave a desired pattern of conductive pathways. The pattern of conductive pathways is typically formed by providing the conductive layer with a resist film, for example containing photosensitive organic monomers. Upon exposure to ultraviolet light, the photosensitive organic monomers polymerize, forming hardened regions. Two types of resists are in common usage today: dry film resists, containing a thin film of photosensitive monomers covered by a ultraviolet-transparent protective film, and liquid resists, also containing photosensitive organic monomers, often present in a solution allowing application as a liquid.
Once the resist has been applied to the conductive layer, the resist is photo-imaged, i.e., selectively exposed to an appropriate ultraviolet light source. An imaging mask is interposed between the source of ultraviolet light and the circuit board containing the resist. The imaging mask includes an ultraviolet-opaque member having an ultraviolet-transparent pattern therein. Accordingly, when the circuit board is photo-imaged only those regions corresponding to the ultraviolet-transparent pattern will be exposed and polymerized.
Subsequent to imaging, the unexposed, and therefore un-polymerized regions of the resist are removed, as through the use of appropriate solvents. The regions of the conductive layer not protected by the polymerized resist are then removed using an acid or alkaline solution. Once the resist has been removed, the non-conductive substrate is left containing the conductive layer in the pattern corresponding to ultraviolet-transparent pattern of the imaging mask.
Additive processes for the manufacture of printed circuit boards typically begin with a non-conductive substrate upon which conductive pathways are selectively added. Consistent with a conventional additive process, a non-conductive substrate containing a resist layer, such as those employed during subtractive methods. The substrate bearing the resist layer is imaged with a negative photo-resist, wherein only those regions corresponding to the desired pattern of conductive pathways remains unexposed. Accordingly, when the resist is developed, i.e., the un-polymerized resist is removed, the non-conductive substrate is exposed in the regions corresponding to the desired conductive pathways. Plating the exposed portions of the non-conductive substrate with a conductive material, and then removing the polymerized regions of the resist completes the process.
A process for the manufacture of either single sided or double sided printed circuit boards according to a general scheme wherein, a substrate including a conductor may sequentially be pre-treated, through holes drilled and made conductive, e.g., for later assembly in a multi-layer circuit board, and then have a first etch resist mask or pattern mask applied to a first side of the substrate. The first etch resist mask may thereafter be set. A second etch resist pattern mask may then be applied to a second side of the substrate, and also set. The substrate having an etch resist mask applied to respective surfaces of the substrate may then be etched to remove any exposed portions of the conductor. Following etching, the etch resist pattern masks may then be removed from the substrate, leaving conductive traces corresponding to portions of the conductor covered by the etch resist mask during the etching process.
The process consistent with the present invention may advantageously be employed for the manufacture of multi-layer laminated circuits. Accordingly, a plurality of individual printed circuit boards manufactured by the process herein may be laminated into a composite structure, wherein the individual printed circuits are generally isolated one from another by interleaved insulating layers.
The present invention also relates to a method of forming a printed circuit wherein a substrate including a thin xe2x80x9cbackgroundxe2x80x9d conductor may sequentially be pre-treated, have through holes drilled and made conductive, and then have a plating resist mask applied to both sides of the substrate, with each of the plating resist masks being set on the substrate following application thereof. After plating resist mask has been applied to the substrate, the substrate may be plated, wherein regions of the substrate not covered by plating resist masks are plated. Subsequent to plating, the plating resist mask is removed from the substrate, and the thin xe2x80x9cbackgroundxe2x80x9d conductor may be etched away. By this process, only those regions that were previously plated, i.e., those regions not covered by the plating resist mask, remain conductive as a result of the built up thickness of these regions.
The present invention also pertains to an apparatus for printing a pattern mask or a conductor onto a substrate. According to a first embodiment, the apparatus comprises a support roller disposed adjacent to print head of a printer used to apply the pattern mask. A substrate may be flexed over the support roller, whereby the substrate achieves a convex geometry relative to the print head. According to this embodiment, a portion of the substrate to which the pattern mask or conductor is instantly being applied may be maintained at a constant distance to the print head.
According to another embodiment, the apparatus consistent with the present invention comprises a compliant member disposed on a rigid member. The compliant member may be disposed adjacent to a print head of a printer used to apply a pattern mask/conductor to a substrate. The compliant member is preferably spaced from the print head a distance to accommodate a substrate therebetween. The apparatus further comprises a mechanism for retaining a substrate to the compliant member, whereby the substrate may be allowed to move relative to the print head in a direction that is orthogonal to a plane tangent to the print head at the point of printing.
Furthermore, the present invention relates to a method of printing a pattern mask or conductors to a substrate, such as an etch resist mask applied to a conductive layer on a substrate or a plating mask applied to a surface of substrate. The method consistent with the present invention includes printing a first pattern mask to the substrate, or a conductive layer disposed thereon. Subsequent to printing the first pattern mask, the position and/or orientation of the first pattern mask is detected. Alternatively, the substrate may be held in a fixed orientation on a substrate feed system, whereby the position and orientation of the first pattern mask is prevented from shifting from a known position. The position an orientation of the first pattern mask may be know by the fixed orientation of the substrate, or may be detected using such techniques as optical scanning or laser scanning the surface of the substrate in order to determine the precise placement and orientation of the first pattern mask. Based on the detected position and/or orientation of the first pattern mask, a second pattern mask or conductor is printed onto the substrate. The second pattern mask may be printed in register with the first pattern mask, or in complimentary manner relative to the first pattern mask. Consistent with this method, the second pattern mask may be precisely positioned on the substrate in order to accommodate any positional and/or orientation errors that may have occurred during the printing of the first pattern mask.